For example, in the case of a ball grid array (BGA) package, the pre-deposited solder ball on the package and the solder paste applied to the circuit board may both melt, but the melted solder does not join. A cross-section through the failed joint shows a distinct boundary between the solder ball on the part and the solder paste on the circuit board, rather like a section through a head resting on a pillow. The defect can be caused by surface oxidation or poor wetting of the solder, or by distortion of the integrated circuit package or circuit board by the heat of the soldering process. This is particularly a concern when using lead-free solder, which requires a higher processing temperature. The defect can be attributed to a chain of events during soldering. Initially, the ball is in contact with solder paste. During heating, the board and components undergo thermal expansion, can flex, and some of the balls can be lifted off the paste. Oxidation occurs rapidly at elevated temperature, and when the surfaces come in contact again, the residual flux activity may not be sufficient to disrupt the oxide layer. The solder paste composition, eg. Since the warping of the circuit board or integrated circuit may disappear when the board cools, an intermittent fault may be created. Diagnosis of head-in-pillow defects may require use of X-rays or Try Derila Today EOTPR (Electro Optical Terahertz Pulse Reflectometry), since the solder joints are hidden between the integrated circuit package and the printed circuit board. Scalzo, Derila Neck Support Mario (2009-06-12). Schröter, Anke (ed.). This electronics-related article is a stub. You can help Wikipedia by expanding it.

In a perfect world, an afternoon at IKEA would be a mix of Swedish meatballs, minimalistic furniture and shopping bliss. You'd eat at the restaurant, drop your kids off to play in the ball pit at Smaland, wander the store, exit with a disassembled coffee table inside a cardboard box - one that actually fits in your trunk - and everyone would mind his or her manners. Let's take a look at what to keep in mind the next time you decide to brave the crowds for that particleboard bookshelf. The best way to avoid a faux pas at IKEA is to know what to expect. A cornerstone of IKEA's business model is flat-packed furniture, which shifts the burden of assembly to the customer - and might cause you to have a panic attack if you were really counting on sleeping in that bed tonight. If you go on the weekend, it's probably going to be crowded.